The present invention relates to an engineered crack-resistant paper or board, as well to a process of producing the paper and/or board. More specifically, the present invention relates to a crack-resistant, flaw-carrying paper and/or board that will have excellent runability.
Paper or board being produced with crack resistance, crack retardation, or fracture impedance is a growing requirement for many board or paper coated laminate structures. The structures are formed into various end uses such as containers, board, packaging, ovenable materials, coated paper, and the like. In particular, it is an objective to produce a tougher paper or paperboard.
There does exist prior patents which disclose various coating layers on base sheets. None are directed to impregnation in geometrical formation.
U.S. Pat. No. 2,515,340 addresses the deposition of a polymer layer over an entire web. The objective of the patent is to make paper and paperboard resistant to wet rubbing and to the coloring of coated paper and paperboard in various selected colors.
U.S. Pat. Nos. 5,004,643; 5,209,964; 5,418,051 and 5,876,792 relate to flexible porous webs which contain an internal coating of a silicone polymer composition. The patents discuss the use of pressurized impregnation methods. These patents focus on process related issues and deal with the “heavy saturation or impregnation with a polymer material” within textile, woven type configurations. They concentrate on encapsulating fibers used for forming webs. They do not discuss or suggest improvements in toughness, or mechanical performance of a cellulose fiber network web. The patents disclose rod-like fibers rather than tube-like fibers, on non-woven networks which are the focus of the underlying invention.
On the other hand, it is an objective of the invention to engineer paper and/or board capable of providing superior crack resistance or crack retardation mechanisms, thereby enhancing the product's fracture toughness and structural integrity. More particularly, geometric formations in the form of a thin discontinuous thermoplastic or thermosetting polymer film that penetrates a cellulose fiber network to provide islands that serves as a mechanism for crack retardation and fracture impedance.
It is a further objective of the invention to improve the overall mechanical performance of the paper or paperboard, thus impregnated.
It is another objective of the present invention to produce paper and/or board grades with improved runability and with the minimization or elimination of web failures which arise from the presence of defects in paper and the propagation of cracks.